1. Field of the Invention
This invention relates to an apparatus for controlling a tension of a sheet delivered from a reel or the like.
2. Prior Art
Generally, a tension of a sheet delivered from a reel, for example, of a sheet cutter, a winder or the like, is measured, and in accordance with the measured tension, a braking force applied to a shaft of the reel around which the sheet is wound is adjusted, thereby controlling the tension of the sheet to the optimum level. The tension of the sheet is measured through a torque exerted on the shaft of the reel. Sensors for measuring such torque are disclosed in Japanese Patent Application Nos. 57-42424, 57-196192 and 57-220549. However, with the conventional tension control apparatus employing such torque sensor, the tension control of the sheet can be carried out satisfactorily only when the sheet is delivered from the reel at a constant speed or when the speed of delivery or movement of the sheet is changed quite gradually. And, when the delivery speed is changed abruptly, that is to say, the sheet is subjected to undue acceleration or deceleration, the tension of the sheet can not be controlled properly due to the moment of inertia (GD.sup.2) of the roll of sheet wound around the reel.